發(fā)布時(shí)間：2018-05-14 18:42

  本文選題：電離層 + 多徑效應(yīng)��； 參考：《西安電子科技大學(xué)》2014年碩士論文

【摘要】：隨著現(xiàn)代戰(zhàn)爭中各種新型武器的應(yīng)用和發(fā)展,主要受地球曲率限制的常規(guī)雷達(dá)已無法適應(yīng)對遠(yuǎn)距離、超低空等目標(biāo)的探測需求,因此各種體制的超視距雷達(dá)成為世界各國爭相研究的重要探測設(shè)備之一。其中,利用電磁波經(jīng)電離層折射的高頻天波超視距雷達(dá)以其特有的大范圍遠(yuǎn)距離探測、多目標(biāo)探測、隱身和超低空目標(biāo)探測等特點(diǎn)成為許多國家的研究重點(diǎn)。然而,由于高頻天波超視距雷達(dá)利用后向返回散射傳播機(jī)理對遠(yuǎn)距離目標(biāo)進(jìn)行下視探測,其采用高頻段的電磁波,信號通道為電離層媒質(zhì),因此其性能必定會受到高頻段內(nèi)的外部有源干擾、電離層媒質(zhì)和下視探測方式等引入的無源干擾等因素的影響。其中,電離層媒質(zhì)信道引起的電磁波多徑效應(yīng)會嚴(yán)重影響雷達(dá)的檢測精度。因此,研究天波超視距雷達(dá)多徑信道均衡方法,消除或降低多徑效應(yīng)引起的信號污染,進(jìn)而提高雷達(dá)檢測性能具有重要的現(xiàn)實(shí)意義和實(shí)用價(jià)值。本文針對高頻天波超視距雷達(dá)應(yīng)用中的多徑效應(yīng)對雷達(dá)檢測性能的影響現(xiàn)實(shí),首先通過分析作為雷達(dá)信道的電離層的基本特性、利用電離層傳播的傳播模式和傳播特性等,討論了多徑效應(yīng)對雷達(dá)回波(距離、多普勒頻移和多普勒展寬)的影響情況。然后,為了抑制或減小多徑效應(yīng)對雷達(dá)回波的影響,采用了信道卷積來對消其影響的信道估計(jì)和均衡方法。在信道估計(jì)與信道均衡中通過建立信道估計(jì)與信道均衡的信號模型,采用了基于訓(xùn)練序列的多徑信道估計(jì)方法與以最小均方誤差為準(zhǔn)則的信道均衡方法,仿真并分析了信道估計(jì)與信道均衡的效果和性能。針對信道均衡后出現(xiàn)的輸出信號旁瓣較高的情況,采用了增加失配濾波器的方法來進(jìn)行旁瓣抑制,并通過加權(quán)迭代最小二乘算法來求解失配濾波器參數(shù),同時(shí)也對多徑信道均衡后再增加失配濾波器后的輸出信號的響應(yīng)和效果進(jìn)行了仿真和分析。之后,提出通過增加均衡長度進(jìn)行旁瓣抑制并與失配濾波器法進(jìn)行效果對比仿真,并針對多徑信道估計(jì)、信道均衡和失配濾波器等過程中可能出現(xiàn)的誤差,分別從信道均衡參數(shù)變化、失配濾波器參數(shù)變化和多徑信道讀取誤差等方面對輸出信號的影響進(jìn)行了仿真和分析,以便于所提出的信道均衡方法在實(shí)際工程中的有效應(yīng)用。最后,給出了本文研究的結(jié)論,并提出了今后進(jìn)一步研究的方向。利用本文提出的多徑信道均衡方法,可以達(dá)到減小多徑效應(yīng)對天波超視距雷達(dá)回波信號影響的目的,提高雷達(dá)對目標(biāo)的檢測能力。
[Abstract]:With the application and development of various new types of weapons in modern warfare, conventional radars, which are mainly limited by the curvature of the earth, have been unable to meet the detection needs of targets such as long-range, ultra-low altitude, etc. Therefore, various systems of OTH radar have become one of the most important detection equipments in the world. Among them, the high frequency sky-wave over-the-horizon radar, which is refracted by the ionosphere, has become the research focus in many countries because of its unique characteristics of large range long-range detection, multi-target detection, stealth and ultra-low altitude target detection. However, because the high frequency sky-wave over-the-horizon radar uses the backward backscattering propagation mechanism to detect the long-range target, it uses the electromagnetic wave in the high frequency band, and the signal channel is the ionospheric medium. Therefore, its performance is bound to be affected by the external active interference in the high frequency band, the passive interference introduced by ionospheric media and the down-looking detection method, and so on. The multipath effect of electromagnetic wave caused by ionospheric medium channel will seriously affect the detection accuracy of radar. Therefore, it is of great practical significance and practical value to study the multipath channel equalization method of sky-wave over-the-horizon radar, to eliminate or reduce the signal pollution caused by multipath effect and to improve radar detection performance. In this paper, the influence of multipath effect on radar detection performance in the application of high-frequency sky wave over-the-horizon radar is discussed. Firstly, the basic characteristics of ionosphere as radar channel are analyzed, and the propagation mode and propagation characteristics of ionospheric propagation are used. The influence of multipath effect on radar echo (range, Doppler shift and Doppler broadening) is discussed. Then, in order to suppress or reduce the influence of multipath effect on radar echo, channel convolution is used to eliminate the influence of channel estimation and equalization. In channel estimation and channel equalization, the signal model of channel estimation and channel equalization is established, and the multipath channel estimation method based on training sequence and the channel equalization method based on minimum mean square error are adopted. The effect and performance of channel estimation and channel equalization are simulated and analyzed. In view of the high sidelobe of output signal after channel equalization, the method of adding mismatched filter is used to suppress the sidelobe, and the parameters of the mismatched filter are solved by the weighted iterative least square algorithm. At the same time, the response and effect of output signal after multipath channel equalization are simulated and analyzed. Then, the sidelobe suppression is proposed by increasing the equalization length and the simulation results are compared with the mismatched filter method, and the possible errors in the multipath channel estimation, channel equalization and mismatch filter are analyzed. The effects of channel equalization parameters, mismatched filter parameters and multipath channel reading errors are simulated and analyzed, respectively, in order to facilitate the effective application of the proposed channel equalization method in practical engineering. Finally, the conclusion of this paper is given, and the direction of further research is proposed. The multipath channel equalization method proposed in this paper can reduce the influence of multipath effect on the echo signal of sky-wave over-the-horizon radar and improve the detection ability of radar to target.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN958.93

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